Agronomic efficiency and residual effect of a novel source of boron for tropical soils

Abstract

Boron (B) deficiency limits yields in many croplands worldwide, particularly in high rainfall regions. However, it is very challenging to evenly deliver the low recommended rates over large areas, especially with the narrow window between deficiency and toxicity in plants. The Brazilian Cerrado is one of the most significant agricultural regions worldwide, but the soils are naturally impoverished in nutrients because of the weathering process. Due to the high rainfall regime in this vast tropical area, B leaching is likely to occur and limit potential yields. This study evaluated the residual effect and the agronomic efficiency of a novel B source for two crops on a Cerrado soil under glasshouse and field conditions. Crops were selected based on their representativeness in the region, as follows: soybean as the first crop and corn as the second. Different sources of B combined with muriate of potash (MOP) for even nutrient distribution were applied to soils and leaching was forced at the glasshouse trial, before planting the first crop. After the first crop harvest, corn was planted as a second crop without B fertilizing, to evaluate the different sources residual effect. Boron sources included a novel fertilizer in its old formulation as fast-release B source (B as sodium borate) and a new formulation as a fast- and slow-release B source (B as sodium borate and colemanite) for season-long B availability to the plant and to prevent B losses. The new B source provided a reduction of B leaching (~69%), compared with the old formulation of the B fertilizer (~82%) and colemanite (~74%). For soybean, there was no statistical difference among the different B sources on the average number of seeds and number of seeds per pod, as well as on grain yield for soybean, but the new fertilizer formulation presented a higher uptake efficiency than the old formulation, under glasshouse conditions. The second crop - corn - showed higher stalk B contents for the lower solubility sources, but no statistical difference for dry matter contents, as well as the number of corn ears and corn ear weight, showing that the residual effect was not enough to provide a statistical difference in production parameters. Under field conditions, the different sources of B showed no difference in dry matter and yield levels in the flowering stage, although less soluble sources of B provided a greater B content in the pods. The second crop - corn - was affected by frost, which interrupted the trial before the maturity stage of the plants, yet there was no statistical difference in total shoot uptake and dry matter weight. The different B sources had no residual effect on the tested field conditions.